How are sprue cutters manufactured?
The jaws and handles of sprue cutters can either be made as one piece, as is normally the case with thin sprue cutters designed for cutting soft material, or separately, which is more common with larger, heavy duty sprue cutters designed to cut harder, thicker material.
There are two methods of manufacturing the basic shape of the jaws and handles of sprue cutters: forging and stamping.
What is forging?
Forging is a manufacturing process that deforms a metal rod or billet workpiece between two dies (a kind of mould).
This can be done by either impacting one of the dies or applying a very high pressure to the dies in order to compress the workpiece between them.
Unlike other manufacturing methods such as casting, during the forging process, as the metal is compressed into the desired shape of the part, the grain structure within the metal is also forced to follow the same shape. This aligning of the grain structure results in a strengthening of the part produced.
As the workpiece is compressed between the two dies some of the material is pushed out between the two dies. This is called flash. This flash then has to be removed by a subsequent machining process.
Forging can be performed with either a hot or cold process. However, forging of steel is nearly always performed using the hot process which involves heating the metal rod or billet that is to be forged. By heating the workpiece it not only becomes easier to compress it to the desired shape but also prevents the resulting part from becoming too strong, which would make the subsequent machining difficult.
Once the machining of the flash has been carried out and the final shape of the part achieved, it can then have the cutting edges ground onto the jaws before being heat treated and tempered to give it the required physical properties, such as hardness, for use as a sprue cutter.
What is stamping?
Stamping is a range of manufacturing processes used with sheet metal. The two forms of stamping that are used to make sprue cutters are blanking and bending.
What is blanking?
Blanking is a shearing (cutting) process that cuts the outline of the part you want from a sheet of metal in a single step. It is performed using a punch and die. The sheet metal is placed between the punch and die, the die has a cut-out shaped to the outline of the desired part, and the punch is the same shape as the cut-out in the die.
As the punch and die are forced together a sheering (cutting) action between the punch and die removes a section of the sheet metal. This section is called a blank, which is how the process gets its name.
What is bending?
As its name suggests, bending is a manufacturing process used to shape a part by bending it to the desired shape. Like blanking, bending uses a punch and die, but unlike blanking the die does not have a cut out. Instead the die is formed to the outside shape of the bend required and the punch is formed to the inside shape of the bend.
As the two are brought together the sheet metal workpiece is bent between them. A workpiece may undergo several bending operations to achieve the final shape. Once this shape is achieved the part can have the cutting edges applied and be heat treated and tempered to produce the necessary physical properties such as strength and hardness.
Which is better: stamping or forging?
The answer to this depends on the type of material and size of the part you will be using the sprue cutter on. Forged sprue cutters will be stronger and harder and so are better suited for removing parts made of hard materials such as platinum and steel, but they will have thicker jaws that would make them unsuitable for removing small delicate parts, whereas stamped sprue cutters will have thinner jaws better suited to removing small, tightly-packed parts from a sprue made of a soft material such as plastic.
How are cutting edges applied?
Once the basic shape of the handles and jaws have been formed by either forging or stamping, the cutting edges can be applied in a further machining process. The process used to apply the cutting edges to the inside of sprue cutter jaws is called grinding.
What is grinding?
Grinding is the process of using a bonded grinding wheel made of abrasive particles to remove material from a workpiece. The grinding wheel is a disc that is spun at high speed, and the workpiece is passed across the side face or circumference surface. Grinding can be done with discs made with grain sizes ranging from 8 (coarse) to 250 (very fine). The finer the grain size, the better the surface finish on the workpiece will be.
What is heat treating and tempering?
Heat treating and tempering are manufacturing processes used to alter the physical properties of metal and other materials. Heat treating involves heating the metal up to a very high temperature and then quenching (rapidly cooling) it. This increases the hardness of the metal, but will also make it more brittle.
Tempering is performed after heat treating, and also involves heating the metal, but to a lower temperature than heat treating, then letting it cool slowly. Tempering will decrease the hardness and brittleness of the metal, and at the same time increase its toughness.